This application is for a component that is used to repair or restore structural and pressure retention integrity of pressure retaining items. Pressure retaining items include but are not limited to items referred to as pressure vessels, tanks, towers, boilers, reactors, heat exchangers, pipe, pumps, and valves. Pressure retaining items are generally constructed of metallic material. Methods of construction of pressure retaining items include welded construction, bolted construction, riveted construction, and a completed pressure retaining item may be constructed using one or various combinations of welded, bolted, or riveted construction. Various industry Codes and Standards provide construction, operation, and inspection requirements pertaining to pressure retaining items in the United States. These include Codes and Standards published by various organizations including but not limited to the American Society of Mechanical engineers (ASME), American National Standards Institute (ANSI), Tubular Exchanger Manufacturers Association (TEMA), American Petroleum Institute (API), and National Board Inspection Code (NBIC). Local jurisdiction authorities (State, Commonwealth, or City) may require compliance with an industry Code or Standard or a combination of Codes and Standards. Pressure retaining items contain fluids (gases or liquids) under a pressure that may be either internal (a pressure acting on the inside of a pressure retaining item) or external (pressure acting on the outside of a pressure retaining item). Pressure retaining items are used to contain, move, or process various fluids. Commercial and government industries using pressure retaining items include but are not limited to chemical, petrochemical process, food, pharmaceutical, water, oil, gas industries, electrical power generation (fossil, hydro, and nuclear), government energy and nuclear process facilities, and various manufacturing industries.
Pressure retaining parts of pressure retaining items way be subjected to material degradation (where degradation is defined as a change in state from that originally intended to the extent that an item that is identified as degraded is not capable of meeting one or more intended purposes). Degradation of material may include thinning of a material, cracks forming within or upon the surface of a material, pitting of a material, or general overall structural damage in a material. Degradation of a material, including material thinning, pitting or cracking, may be caused by but is not limited to erosion or corrosion. Material degradation can occur from a chemical reaction between the fluid contained by a pressure retaining item and its material of construction. Material degradation can occur due to movement or impingement of fluid against pressure retaining material of construction of a pressure retaining item. Corrosion, erosion or other mechanisms, either individually or in combination, can result in degradation of material that is required to maintain the structural and pressure retaining capability of pressure retaining items. Degradation of a material, including material geometrical changes or changes in a material physical property including but not limited to changes in material yield strength, tensile strength, modulus of elasticity, etc., may be caused by an imposed load, pressure, or temperature condition. Material degradation can be global (by global it is meant that essentially all or a large portion of the materials of construction of a pressure retaining item are subjected to material degradation). Alternatively, material degradation can be local (by local it is meant that a small amount of the total materials of construction of a pressure retaining item subjected to material degradation). Either global or localized material degradation can result in a potential hazardous operating condition wherein as-designed and constructed safety factors against fluid leakage or pressure retaining item structural integrity or pressure retaining item pressure boundary pressure retention capability are reduced. In severe material degradation conditions (either global or local), failure of pressure retaining items can occur. Pressure retaining item failure can result in affecting the safety of personnel safety and/or in economic losses.
To obtain information pertaining to material degradation occurring in pressure retaining items periodic inspections of pressure retaining items are performed. Inspection methods include visual inspection for observation of material degradation or visual inspection for observation of fluid leakage. Inspection methods also include pressure retaining item material of construction thickness measurements for determination of material degradation. Thickness measurements can be obtained using various data collection and nondestructive examination methods including but not limited to physical measurements using various gages or measuring instruments or by performing ultrasonic examination to obtain material condition and thickness information.
Where material degradation is determined, assessments of remaining life and adequacy of pressure retaining item to remain in service while continuing to operate within the requisite factors of safety are performed. Where it is determined that a specific pressure retaining item does not have the requisite factor of safety to continue operation several options are available including 1) changing the conditions under which that specific pressure retaining item is operated to conditions that are acceptable for continued safe operation, of 2) replacing or repairing unacceptable parts of pressure retaining items.
Common methods of repair include removal of a material section determined to be unacceptable and replacement with a new section of material of equivalent or better structural, pressure retaining, and/or corrosion and/or erosion resistance than that used in the original construction. New sections of replacement material are most often installed by joining them to an existing pressure retaining item at locations with adequate material thickness for continued operation of the item using full or complete penetration welds. This type of repair may be referred to as a “flush patch repair”.
A different type of repair used where a section of material degradation may be localized is referred to as “weld build-up repair”. A “weld build-up repair” is a repair method wherein weld metal is deposited on to the area of unacceptable material to return the material to a condition wherein the pressure retaining item can be returned to service under a specific set of operating conditions.
As often considered but not generally allowed by some Codes or Standards that govern the construction, operation, and inspection of pressure retaining items, or that may not be allowed a jurisdictional authorities (State, Commonwealth, or City) is a method of repair referred to as a “fillet welded patch plate” repair. In this type repair, a section of new material is fit over a local area of a specific pressure retaining item at the location of unacceptable material and joined to the surface of that specific pressure retaining item using a fillet weld. This method of repair does not readily allow for volumetric examination or pressure integrity examination of the completed fillet weld joint and the completed repair may result in a smaller factor of safety than either a “flush patch repair” or “weld build-up” repair”.
“Flush patch repair” and the “weld build-up repair” methods of repair or restoration are generally allowed by governing Codes and Standards for construction, operation, or inspection, and are also generally allowed by most jurisdictional authorities (State Commonwealth, or City) in the United States. “Flush patch repair’ and the “weld build-up repair” methods of repair allow for a volumetric examination and pressure integrity examination of the welds used in a completed repair. “Flush patch repair’ and the “weld build-up repair” methods may result in equal or greater pressure retention and structural integrity factors of safety to those that existed at the time of original construction. “Flush patch repair” or “weld build-up repair” methods for repair of pressure retaining items have several limitations or negative aspects including but not limited to:
“Flush patch repair or” “weld build-up repair”:                1. require removal of pressure retaining items from service        2. require cutting out of pressure retaining item local material degraded areas (“flush patch repair” only)        3. require preparation of pressure retaining item remaining material for welding of the new replacement section of material or weld buildup by cutting or grinding.        4. require exact cutting, curvature fabrication (by rolling, forming, or machining) and weld end preparation of the new section of material for fit-up (“flush patch repair” only).        5. may require use of weld joint backing strips. The backing strips may or may have to remain in place depending on their accessibility after welding. If left in place they may contribute to a reduction in a pressure retaining item factor of safety or even worse the acceleration of new local areas of corrosion or erosion due to the introduction of a new fluid flow path obstruction (“flush patch repair” only).        6. may expose personnel to lethal or hazardous fluid contents of a pressure retaining item such as chemical, gas, or radioactive fluid contents.        7. introduce the potential for damage to internal parts of pressure retaining items such as damage to tubes of heat exchangers.        8. introduce the potential for intrusion of foreign materials into the internals of pressure retaining items.        9. may require hydrostatic or pneumatic testing of a. pressure retaining item to insure pressure retaining integrity has been maintained due to breach of pressure boundary.        10. may only be allowed on the inside surface of a pressure retaining item or may only be allowed on the outside surface of a pressure retaining item depending on governing code or jurisdictional authority requirements.        